in the end, you’re leeching off a service you enjoy.
I don’t think that’s a fair or true statement.
For one thing, the “service” here has risen to a point of ubiquity that it’s a de facto public space. Everything is on YouTube – legacy media channels, individual enthusiasts, alternative media outlets, the worlds of tech, fashion, politics, sports – you name it. If you were deprived of all access to it, you would have a qualitatively poorer access of what is going on in society. So it’s not equivalent to a traditional service like a trade.
For another, blocking ads is not merely refusal to pay a fee of some kind. Advertisements are cognitively intrusive, designed to affect your willpower and decision-making, used to track and control your behaviour, compromise your digital safety, and turn you into a product for companies to whom you do not give your consent for the opportunity to be exploited. Blocking that system of “payment” is not simply prudent but right, and the choice between paying a monetary fee or being so exploited is not a fair choice at all.